<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style type="text/css">
        .main {
            width: 1200px;
            height: 2000px;
            margin: 0 auto;
            background-color: pink;
        }
        .slider {
            width: 100px;
            height: 300px;
            background-color: green;
            position: fixed;
            left: 50%;
            top: 100px;
            margin-left: 610px;
        }
    </style>
</head>
<body>
    <div class="main">
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
        <h1>123</h1>
    </div>
    <div class="slider">
    </div>
</body>
</html>